There are so very many things that can be unusual about our tears. Which one(s) actually contribute to our discomfort, though? That’s the question that no one can really answer. It is a puzzle we have to work out over time.

Anyway, this is a nice study looking into differences in the bacteria on the eye surface and comparing ‘normal’ cases with type 2 diabetes mellitus. Yes, they are different.

How Ocular Surface Microbiota Debuts in Type 2 Diabetes Mellitus. Li et al, Front Cell Infect Microbiol. 2019 Jun 17;9:202.

High glucose represents a good environment for bacterial growth on the skin, on the ocular surface (OS) and in the tears of type 2 diabetes mellitus (T2DM) patients, affecting the conjunctival bacterial community. This study aimed to investigate the OS bacterial flora of T2DM patients and healthy subjects using 16S rRNA sequencing-based bacterial identification. Among 23 healthy subjects (CON) and 31 T2DM patients, 54 eyes were examined to investigate the OS bacterial community. Factors potentially affecting the microbial growth were controlled. Results showed the OS microbiota presented higher diversity in the T2DM group than in the CON group. Bioinformatic analysis showed a lower abundance of Proteobacteria and a higher abundance of Bacteroidetes at the phyla level as well as a significantly increased abundance of Acinetobacter and Pseudomonas at the genus level in the T2DM group. The difference in OS microbiota at taxonomic level was associated with Ocular Surface Disease Index and course of T2DM. These findings indicate the OS flora in T2DM patients is significantly different from that in healthy subjects, which may be closely associated with OS discomfort and course of T2DM.